Lithographic printing process

ABSTRACT

Directing gas, e.g., air, at the surface of a lithographic plate (in an amount insufficient to dry the plate) after the image transfer step but before wetting and inking in the next press cycle, provides an additional means for controlling print density and increasing press latitude.

United States Patent Inventors Doyle O. Etter;

David J. De Marie, both or Rochester, N.Y. 7

Nov. 3, 1969 Dec. 28, 1971 Eastman Kodak Company Rochester, N.Y.

Appl. No. Filed Patented Assignee LITHOGRAPHIC PRINTING PROCESS 9 Claims, 1 Drawing Fig.

U.S.Cl l0l/450, 101/142 Int. Cl 841m l/06, B41f9/18 Field ofSearch ..101/141-145, 450-452 [56] References Cited UNITED STATES PATENTS 2,002,815 5/1935 Harrold 101/141 643,372 2/1900 Cornwall 101/141 2,503,758 4/1950 Murray..... 101/450 X 2,676,536 4/1954 Ste-Marie. 101/141 2,884,855 5/1969 Koch 101/142 FOREIGN PATENTS 685,938 1/1953 Great Britain 101/141 Primary Examiner-Clyde L. Coughenour An0rneysWal1er O. Hodsdon and Dwight J. Holter ABSTRACT: Directing gas, e.g., air, at the surface of a lithographic plate (in an amount insufficient to dry the plate) after the image transfer step but before wetting and inking in the next press cycle, provides an additional means for controlling print density and increasing press latitude.

PATENTEU mam l97l 3.830.149

DOYLE 0. 5775/? DAV/D J. DeMA/PLE INVENTORS aw/W QM A TTORNEYS LITHOGRAPHIC PRINTING PROCESS This invention relates to lithographic printing. In one of its aspects this invention relates to methods of lithographic printing in which the criticality of control of the wetting and inking stages is substantially decreased.

The increasing public demand for all types of written and printed materials has placed a heavy demand on the printing industry. Because of the quality and relative speed with which they are utilized, lithographic techniques have assumed an increasingly important role in meeting this demand. These lithographic methods normally involve the use of a substantially planar printing plate which has a printing surface which is hydrophilic (ink repelling) in background areas and hydrophobic in image areas.

In the printing operation the processed plate is mounted on the master cylinder which then is rotated through a printing cycle sufficient times to produce the desired number of copies. The printing cycle usually involves wetting the plate to assure that the background areas will not hold ink and applying ink to the plate image areas. The plate is then pressed into contract with a receiving element, normally a blanket roller, which in turn contracts the ultimate receiving layer. Obtaining and maintaining the proper ink-water balance is often extremely difficult. For this reason, and because of the fine detail such plates are to record, etc., the effective use of lithographic techniques has been substantially limited to highly skilled artisans.

In an effort to enhance the ability of the lithographic industry to keep pace with the demands placed upon it, extensive investigations have been undertaken to simplify the lithographic process and thereby make it more generally available. Accordingly, the industry has been provided with new lithographic plates, automated equipment for preparing lithoplates, improved and simplified solutions for use in processing plates or for use on the press, improved inks, etc. The use of these improved systems, although simplifying lithography somewhat, still is involved with critical aspects which require high skill on the part of the press operator.

We have found that by directing a gaseous stream at the plate surface during a press run between the transfer step and the wetting and inking step of the next press cycle, a new control means is afforded the press operator. This new control means renders the ink-water balance less critical and provides a simple means for adjusting print density. This method of lithographic printing, including directing a gaseous stream at the printing surface of the lithographic plate also provides a means for increasing the ink-up rate of a plate freshly mounted on the press and increases the overall press latitude of a plate on the press.

Other advantages and objects of the present invention will be apparent from consideration of the present specification including the following description taken together with the drawing. For a more comprehensive understanding of the advantages derived and objects accomplished by the practice of the present invention, reference is made to the drawing which is a schematic view of portions of a lithographic press which illustrates a particularly advantageous embodiment of the present invention whereby lithographic plate 22 having hydrophilic background areas and hydrophobic image areas is mounted on master cylinder for rotation therewith. As master cylinder 20 rotates through a full cycle. it carries the plate through wetting and inking stations which can include a single roller which contacts the lithoplate to simultaneously wet and ink the plate or separate rollers contacting the plate as illustrated wherein water supply roller 12 contacts lithoplate 22 at nip l4 and wets the plate. The wet plate is contacted by inking roller 16 at nip 18. The water provided by water supply roller 12 clings to the hydrophilic areas of lithoplate 22 and assists in repelling the ink so that ink supplied by roller 16 desirably adheres only to the hydrophobic image areas of the plate. As master cylinder 20 proceeds through the cycle, it carries lithoplate 22 into rolling contact with blanket roller 26 at nip 24. At least part of the ink is thereby transferred imagewise to blanket roller 20 which also rotates to bring the transferred image into contact with receiving element 29 which is pressed into contact with the inked blanket roller at nip 28 by pressure roller 30. As receiving element 29, e.g., paper, emerges from nip 28, it desirably has thereon an ink image corresponding to the image on lithoplate 22. As lithoplate 22 continues in the cycle after the transfer of ink to the blanket roller, it passes through pressure area 31 in which a gaseous stream, e.g., of air, from pressure supply and control means 36 through gas supply line 34, emerging through air knife 32, is directed at the plate surface advantageously in the direction of the axis of master cylinder 20. As master cylinder 20 continues to rotate lithoplate 22 is again wetted and inked in the next cycle. The cycle is repeated sufficient times to provide the desired number of copies.

As thus described, the press cycle can involve conventional steps except that the cycle also includes the improvement whereby a gaseous stream insufficient to completely dry the plate is directed at the plate surface after the transfer but prior to the wetting and inking of the next cycle. The force of the gas stream applied to the plate surface can vary widely depending upon the amount of density variation desired, the particular plate employed, etc. However, the gas is desirably supplied from a source that will apply to the plate surface at least that amount which would be provided by a knife opening through which gas at l p.s.i., desirably at least 5 p.s.i., relative pressure is directed about one-eighth inch to the plate surface. The pressure at the plate surface is advantageously at least about 5 p.s.i., but exceptional results can be employed using pressures of at least 10 p.s.i., with even more efiect noted at pressures exceeding 20 p.s.i. The maximum flow of gas is usually dictated by convenience but in any event should be insufficient to totally dry the plate. Some evaporation from the plate surface, however, can be tolerated with no severe detrimental results.

The gas utilized is advantageously air but other gases which are substantially inert to the ink and plate surface may be employed. Such gases of low activity as nitrogen may be employed as well as the more chemically active ozone. It is usually desirable to utilize relatively dry gas but the inclusion of even large amounts of water vapor in the gas appears to have no substantial detrimental effect.

Increasing the temperature of the gas which is utilized results in more pronounced effects on the resultant print density and a similar effect is noted even with little or no gas pressure when high heat is utilized. However, maintaining strict temperature control usually creates additional problems in the press room so gas at about room temperature (about 25 C.) is usually employed.

The gas stream is desirably directed at the lithoplate through an air knife but can be supplied through any convenient channel. It is usually desirable to locate the opening which provides the gaseous stream no more than 1 inch (especially about one-eighth inch) from the plate surface advantageously to provide a large amount of potential for agitation of the liquid or semiliquid residue on the plate surface after the transfer step. The use of an air knife for such purposes makes it possible to attain a relatively uniform gas impingement across the full width of the lithoplate so that as the plate is carried through a full cycle on the master cylinder, the entire printing surface of the plate is subjected to impingement (even though only a small portion at each instant is receiving impingement). Such a knife is advantageously positioned so that the knife opening extends substantially parallel with the axis of the master cylinder (and with the printing surface of the plate) at a distance of less than about 1 inch from the printing surface. The gas flow is desirably directed so that an imaginary line extended in the direction of gas flow would cut a substantial arc in a circle representing the master cylinder. This direction can be varied but it is usually desirable again to produce substantial agitation of the residue on the plate.

The plate materials and presses which may be employed according to the present invention also can vary widely. The use of pressure according to the present invention appears to have a significant effect on the ink-water balance. It is, therefore, apparent that any method using a combination of press and plate materials which depend on an ink-water differential for their effectiveness will be similarly (but perhaps to varying degree) affected by using the improvement of the present invention. Nonetheless, we have found that the methods according to the present invention may be more efiicaciously employed with plates that sometimes are difficult to ink, e.g., plates having gelatin or gelatinous residue on at least a portion of the printing surface.

The following examples are intended to illustrate our invention and/or advantages thereof.

EXAMPLE 1 A lithographic plate material having a silver halide sensitized gelatin emulsion coated on a paper support is exposed in a standard copy camera and developed in an activator for 20 seconds at 70 F., then treated for 20 seconds in a stop bath (as described in US. Pat. No. 3,146,105), and then dried. The dry plate is soaked for 20 seconds in distilled water and then placed on an A. B. Dick Model 360 lithopress. The press is run at number speed using lPl Speed King Ink and distilled water fountain at 0.0035-inch ink hopper opening, number 1 ink setting, and number 22 water setting. The right half of the plate is impinged with room temperature air from a hair drier located about 1 inch from the plate surface downstream (in the rotary direction) from the blanket roller and upstream (before) from the wetting and inking station of the press. The plate inks rapidly to D-max. in the areas receiving impingement but remained almost totally blind in areas receiving no impingement, as demonstrated by relatively clean sharp images on the half of the lithoprints corresponding to the side of the plate receiving impingement with almost no visible image on the print side corresponding to the side of the plate receiving no impingement.

EXAMPLE 2 The procedure according to example 1 is followed except that hot air (about 150 F.) is impinged on the right side of the plate rather than at room temperature. Similar but somewhat more pronounced results are noted.

EXAMPLE 3 The procedure according to example I is followed except that nitrogen supplied from a pressure tank is utilized for the impingement gas. Similar results are noted.

EXAMPLE 4 The procedure according to example 1 is followed except that a 25 fountain setting is employed. Similar results are noted.

EXAMPLE 5 The procedure according to example 1 is followed except that a 25 fountain setting is employed and the air source is directed at the surface from about three-fourths inch. Results similar to but more pronounced than example 1 are noted.

EXAMPLE 6 The procedure according to example I is followed except that the plate employed has an aluminum support with a gelatinous image thereon and a 40 fountain setting is utilized. Similar results to those of example I are noted.

EXAMPLE 7 The procedure according to example i is followed except that the ink employed is Chromatone IDP Offset Trans. Yellow used at a 0.002-inch ink hopper opening and number 40 water opening. Similar results to those of Example 1 are noted.

EXAMPLE 8 The procedure according to Example I is followed except that the full width (the entire plate) in each press cycle is subjected to air impingement at about 5 p.s.i. from an air knife located about one-eighth inch from the plate surface approximately midway in the press cycle between the blanket roller and the wetting and inking station of the next printing cycle. Prints of consistently good density are obtained in a very short time as compared to an identical run except with no air impingement.

EXAMPLES 91 2 The procedure according to example 1 is followed except that the air is supplied to the plate by an air knife, the opening of which is located about one-eighth inch from the plate surface so that air escaping from the knife opening flows in the direction of the axis of the master cylinder and the pressure at the knife opening is maintained at different pressures. The increase in density of the side receiving impingement (as compared to the side receiving no impingement) is noted with respect to a scale having a total of 25 density units. The results are tabulated in table 1 below.

The procedure according to example 10 is followed except that the air supplied to the air knife is bubbled through water to increase the water content of the impinging air. Similar results to those of example 10 are noted.

EXAMPLE 14 The procedure according to example 1 is followed except that ozone supplied from a pressure tank is utilized for the impingement gas. Similar results to those of example l are noted.

The invention has been described in detail with particular reference to preferred embodiments'thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. In a lithographic process comprising a printing cycle which is repeatedly carried out to produce a desired number of lithographic copies, which cycle includes:

a. wetting and inking a lithographic plate; and

b. transferring at least part of the ink to a receiving element;

the improvement wherein the cycle further includes .in addition to steps (a) and (b): c. directing a gaseous stream at the plate after said step (b) but prior to step (a) of the cycle. 2. The invention according to claim 1 and wherein said gaseous stream is supplied at a velocity which would at least be equal to that provided by a knife opening through which about one-eighth inch to the plate surface.

3. The invention according to claim I and wherein said gaseous stream is supplied at a velocity which would at least be equal to that provided by a knife opening through which gas at 5 p.s.i. relative pressure is directed from a distance of about one-eighth inch to the plate surface.

4. The invention according to claim 1 and wherein the relative pressure provided by the gaseous stream at the plate surface is at least about 5 p.s.i.

5. The invention according to claim 1 and wherein said process involves the use of a lithographic press wherein said lithographic plate is mounted on a master cylinder for rotation therewith whereby as the cylinder rotates through its cycle the plate is wetted and inked and is contacted by a blanket roller whereby at least some of the ink is imagewise transferred to the blanket and wherein the gaseous stream which then is directed at the plate prior to the wetting and inking of the next cycle provides a relative pressure of at least 5 p.s.i. at the'plate surface.

6. in a lithographic process involving a lithographic press having a lithographic plate mounted on a master cylinder, said process comprising rotating said master cylinder through a repeating cycle including:

a. passing the lithographic plate through an area in which the plate is wetted and inked; and

b. passing the plate through a transfer area in which at least part of the ink is transferred from the plate to a receiving element; the improvement wherein the cycle further ineludes:

c. passing the plate through a pressure area which is subsequent to the transfer area but prior to the wetting and inking area of the next cycle and in which a gaseous stream is directed at the plate surface in an amount insufficient to totally dry the plate surface.

7. The invention according to claim 6 and wherein said gaseous stream provides a relative pressure of at least 5 p.s.i. at the plate surface.

8. The invention according to claim 6 and wherein said gaseous stream is provided across the entire lithographic plate. through an air knife, the knife opening of which extends substantially parallel with and directed toward the printing surface of the plate and the axis of the master cylinder at a distance of less than about 1 inch from the printing surface of the plate, said gaseous stream resulting in a relative pressure of at least about 5 p.s.i. at the printing surface.

9. The invention according to claim 8 and wherein the gaseous stream consists essentially of air to provide a relative pressure of at least about 10 p.s.i. at the plate surface.

3 3 7 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION mam No. 3,630,149 Dated December 28. 1971';

Inventor(s) D le O. Etter, et a].

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 22, delete "contract" and insert--contact---,.

Column 1, line 23, delete "contracts" and insert-"contacts Column 2, line 2, delete "20 and insert---26--.

Column 4, line 70, insert---next--before the word "cycle".

(SEAL) Attest:

EDWARD M.FLET0HER, JR. ROBERT GOTTSCHALK Attesting Officer- Commissioner of Patents 

1. In a lithographic process comprising a printing cycle which is repeatedly carried out to produce a desired number of lithographic copies, which cycle includes: a. wetting and inking a lithographic plate; and b. transferring at lEast part of the ink to a receiving element; the improvement wherein the cycle further includes in addition to steps (a) and (b): c. directing a gaseous stream at the plate after said step (b) but prior to step (a) of the cycle.
 2. The invention according to claim 1 and wherein said gaseous stream is supplied at a velocity which would at least be equal to that provided by a knife opening through which gas at 1 p.s.i. relative pressure is directed from a distance of about one-eighth inch to the plate surface.
 3. The invention according to claim 1 and wherein said gaseous stream is supplied at a velocity which would at least be equal to that provided by a knife opening through which gas at 5 p.s.i. relative pressure is directed from a distance of about one-eighth inch to the plate surface.
 4. The invention according to claim 1 and wherein the relative pressure provided by the gaseous stream at the plate surface is at least about 5 p.s.i.
 5. The invention according to claim 1 and wherein said process involves the use of a lithographic press wherein said lithographic plate is mounted on a master cylinder for rotation therewith whereby as the cylinder rotates through its cycle the plate is wetted and inked and is contacted by a blanket roller whereby at least some of the ink is imagewise transferred to the blanket and wherein the gaseous stream which then is directed at the plate prior to the wetting and inking of the next cycle provides a relative pressure of at least 5 p.s.i. at the plate surface.
 6. In a lithographic process involving a lithographic press having a lithographic plate mounted on a master cylinder, said process comprising rotating said master cylinder through a repeating cycle including: a. passing the lithographic plate through an area in which the plate is wetted and inked; and b. passing the plate through a transfer area in which at least part of the ink is transferred from the plate to a receiving element; the improvement wherein the cycle further includes: c. passing the plate through a pressure area which is subsequent to the transfer area but prior to the wetting and inking area of the next cycle and in which a gaseous stream is directed at the plate surface in an amount insufficient to totally dry the plate surface.
 7. The invention according to claim 6 and wherein said gaseous stream provides a relative pressure of at least 5 p.s.i. at the plate surface.
 8. The invention according to claim 6 and wherein said gaseous stream is provided across the entire lithographic plate through an air knife, the knife opening of which extends substantially parallel with and directed toward the printing surface of the plate and the axis of the master cylinder at a distance of less than about 1 inch from the printing surface of the plate, said gaseous stream resulting in a relative pressure of at least about 5 p.s.i. at the printing surface.
 9. The invention according to claim 8 and wherein the gaseous stream consists essentially of air to provide a relative pressure of at least about 10 p.s.i. at the plate surface. 